The invention relates to communications systems in general and, more specifically, the invention relates to a video compression technique suitable for use in an interactive multimedia information delivery system.
Over the past few years, the television industry has seen a transformation in a variety of techniques by which its programming is distributed to consumers. Cable television systems are doubling or even tripling system bandwidth with the migration to hybrid fiber coax (HFC) cable plant. Customers unwilling to subscribe to local cable systems have switched in high numbers to direct broadcast satellite (DBS) systems. And, a variety of other approaches have been attempted focusing primarily on high bandwidth digital technologies, intelligent two way set top terminals, or other methods of trying to offer service differentiated from standard cable and over the air broadcast systems.
With this increase in bandwidth, the number of programming choices has also increased. Leveraging off the availability of more intelligent set top terminals, several companies such as Starsight Telecast Inc. and TV Guide, Inc. have developed elaborate systems for providing an interactive listing of a vast array of channel offerings, expanded textual information about individual programs, the ability to look forward to plan television viewing as much as several weeks in advance, and the option of automatically programming a VCR to record a future broadcast of a television program.
Unfortunately, the existing program guides have several drawbacks. They tend to require a significant amount of memory, some of them needing upwards of one megabyte of memory at the set top terminal (STT). They are very slow to acquire their current database of programming information when they are turned on for the first time or are subsequently restarted (e.g., a large database may be downloaded to a STT using only a vertical blanking interval (VBI) data insertion technique). Disadvantageously, such slow database acquisition may result in out of date database information or, in the case of services such as pay per view (PPV) or video on demand (VOD), limited scheduling flexibility for the information provider.
The use of compression techniques to reduce the amount of data to be transmitted may increase the speed of transmitting program guide information. In several communications systems, the data to be transmitted is compressed so that the available transmission bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is also incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
The above-referenced standards describe data processing and manipulation techniques that are well suited to the compression and delivery of video, audio and other information using fixed or variable rate digital communications systems. In particular, the above-referenced standards, and other xe2x80x9cMPEG-likexe2x80x9d standards and techniques, compress, illustratively, video information using intra-frame coding techniques (such as run-length coding, Huffman coding and the like) and inter-frame coding techniques (such as forward and backward predictive coding, motion compensation and the like). Specifically, in the case of video processing systems, MPEG and MPEG-like video processing systems are characterized by prediction-based compression encoding of video frames with or without intra- and/or inter-frame motion compensation encoding.
However, the MPEG-1 and MPEG-2 standards have, in some instances, very strict elementary stream and transport stream formats, causing usage of extra bandwidth for certain applications. For example, if a number of interactive program guide (IPG) pages were created as video sequences, only limited number of pages could be encoded into a transport stream(s) at a specified bandwidth.
Therefore, it is desirable to provide a video compression and decompression technique that enables an increased number of programs (video sequences) to be transmitted within an MPEG-2 transport stream(s).
The invention provides various data structures suitable for efficient representation of program data (e.g., program guide information for a number of groups of channels) having some amount of common (i.e., redundant) information. Depending on the particular program data, redundant textual and/or video information may be present. Pictures containing redundant information may be discarded from processing, and pictures containing non-redundant information may be processed using more efficient coding techniques (e.g., coding of difference frames). The encoding and transmission of reference I frames are also minimized. The removal of redundant information and efficient encoding of transmitted information greatly reduce the bandwidth and/or memory resources needed to transmit and/or store the program data.
An embodiment of the invention provides a data structure for representing program data that includes a number of (video) streams. Each stream comprises a group of pictures (GOP) having a first picture and one or more remaining pictures. The data structure includes a first set of one or more elements for representing data for the first pictures in the GOPs, and a second set of one or more elements for representing data for the remaining pictures in the GOPs. At least one element in the first set represents data for (at least a portion of) the first picture of at least one respective GOP, with each such first picture having been encoded as a reference I picture. Each remaining element (if any) in the first set represents data for (at least a portion of) the first picture of a respective remaining GOP, with each such remaining first picture having been encoded as either a difference picture or a P picture. Each element in the second set represents data for (at least a portion of) a particular remaining picture in one of the GOPs, with each such remaining picture having been encoded as either a P picture, a B picture, or an I picture. Each of the streams is represented by one or more elements in the first set and one or more elements in the second set.
As noted above, various data structures are provided by the invention. In one specific data structure design, the first set includes a number of elements, one element for each of the GOPs. Each element in the first set can represent data for the first picture of a respective GOP encoded as a reference I picture. Alternatively, one element in the first set can represent data for the first picture of one GOP encoded as a reference I picture, and each remaining element in the first set can represent data for the first picture of a respective remaining GOP encoded as a difference picture. The first set can also include a single element for representing data for the first picture of one GOP.
In this specific data structure design, the second set can include a number of elements (e.g., one element for each remaining picture in one particular GOP). The elements in the second set can represent data for a single GOP, with each remaining picture in this GOP having been encoded as either a P picture or a B picture. Alternatively, the elements in the second set can represent data for at least one remaining picture of each of the GOPs.
Each picture of the GOPs can include, for example, a first portion indicative of textual information (e.g., program guide) and a second portion indicative of video information (e.g., a moving video). In a specific implementation, the first and remaining pictures of each GOP share a common first portion, and the first pictures of the GOPs share a common second portion. The text portion can be encoded using a text encoder or an encoder adapted for encoding text.
In another specific data structure design, the elements are used to represent data for GOPs having a common first (e.g., text) portion but each GOP having a second portion (e.g., a video sequence) that may be different from those of other GOPs. The first portion of the first picture of one of the GOPs can be encoded and used as a reference first portion. The second portion of the first picture of each GOP having an unduplicated second portion can also be encoded as a reference second portion for that GOP. The second portion of the remaining pictures in each GOP can then be encoded based on the reference second portion generate for the first picture in the GOP.
The data structures described herein can be used to represent data for a matrix that may include any number of GOPs or streams (e.g., 15 or more), with each GOP including any number of pictures (e.g., 15 or more). The pictures can be encoded using picture-based encoding, slice-based encoding, or some other encoding technique. Also, the encoding can be achieved with a software (e.g., MPEG-2) encoder, a hardware encoder, or a combination thereof. For example, the text portion can typically be efficiently encoded with a software MPEG-2 encoder.
The invention further provides systems (e.g., head-ends) and set top terminals that implement and/or process the data structures described herein.